Remove C::swap(C*) where C = Hash{Map,Set}<T>.

Remove the swap() method over non-reference hash sets and
map arguments, along with their curious OtherType indirection,
the methods aren't of real use.

R=
BUG=

Review-Url: https://codereview.chromium.org/1979843002
Cr-Commit-Position: refs/heads/master@{#393770}
6 files changed